Search results for "Nucleophile"
showing 10 items of 385 documents
Designed Synthesis of New ortho-Carborane Derivatives: from Mono- to Polysubstituted Frameworks
2008
The use of nucleophilic and electrophilic processes allow the designed synthesis of several B-iodinated derivatives of o-carborane. Because of the straightforward Pd-catalyzed conversion of B-I to B-C bond with Grignard reagents, such as methylMgBr and biPhenylMgBr, both, symmetrical 3,6-R 2-1,2- closo-C 2B 10H 10 and asymmetrical 3-I-6-Me-1,2- closo-C 2B 10H 10 could be obtained. Not only conventional reactions in solution have been studied but also a highly efficient, clean and fast solvent-free procedure has provided successful results to regioselectively produce B-iodinated o-carborane derivatives by a careful control of the reaction conditions. The high number of nonequivalent leaving …
The first member of a second generation family of ligands derived from metal-ion assisted reactivity of di-2,6-(2-pyridylcarbonyl)pyridine: Synthesis…
2012
Abstract Nucleophilic attack by the carbanion −CH2COCH3 at the carbonyl carbon atoms of 2,6-di-(2-pyridylcarbonyl)pyridine, pyCOpyCOpy, in the presence of Mnn+ ions under basic conditions has yielded the cationic cluster [Mn4(OH)2(L)2(H2O)2](ClO4)4 (1), where L2− is the (py)C(CH2COCH3)(O−)(py)C(CH2COCH3)(O−)(py) dianion. The cluster cation possesses a planar {MnII2MnIII2(μ3-OH)2(μ-OR)4}4+ rhombus core, resulting from two μ3-OH− ions and two η1:η2:η1:η1:η1:η2:η1:μ3 bridging L2− groups from the in situ formed ligand. Complex 1 is antiferromagnetically coupled with an unusual S = 2 ground state resulting from spin frustration effects within the triangular Mn3 subunits of the cluster.
A density functional theory study for the Diels–Alder reaction between N-acyl-1-aza-1,3-butadienes and vinylamines. Lewis acid catalyst and solvent e…
2002
Abstract The molecular mechanism for the Diels–Alder reaction of N-acyl-1-aza-1,3-butadiene with dimethylvinylamine has been studied using density functional theory methods. This cycloaddition is the nucleophilic attack of the vinylamine to the conjugate position of the unsaturated acyl imine with concomitant ring-closure. The presence of a Lewis acid catalyst coordinated to the acyl oxygen atom decreases markedly the activation energy associated to the nucleophilic attack. This results from an increasing of the electrophilicity of the 1-aza-1,3-butadiene that shift the mechanism from a highly asynchronous concerted process to a polar stepwise one.
A DFT study of the mechanism of Brønsted acid catalysed Povarov reactions
2015
Abstract The molecular mechanism of the Bronsted acid (BA) catalysed Povarov reaction of N -phenyl- C -methoxycarbonyl imine with a methylenecyclopropane (MCP) has been investigated using DFT methods at the MPWB1K/6-31G(d) level. This BA catalysed Povarov reaction is a domino process initialised by the formation of a cationic intermediate which experiences a quick intramolecular Friedel–Crafts reaction yielding the final tetrahydroquinoline. Protonation of the imine nitrogen atom notably increases the electrophilicity of the corresponding species, accelerating the reaction through ionic processes. Analysis of the Parr functions in the initial nucleophilic attack of MCP to the protonated imi…
Fluorinated heterocyclic compounds. A photochemical synthesis of 3-amino-5-perfluoroaryl-1,2,4-oxadiazoles
2001
Abstract A photochemical methodology for the synthesis of 3-amino- (or 3- N -substituted amino) 5-pentafluorophenyl-1,2,4-oxadiazoles is reported. Irradiation of 3-pentafluorobenzoylamino-4-methyl-1,2,5-oxadiazole (Furazan) at 254 nm in methanol and in the presence of ammonia, primary or secondary aliphatic amines produces 3-amino-, 3-( N -alkylamino)-, 3-( N , N -dialkylamino)-5-pentafluorophenyl-1,2,4-oxadiazoles. The photoreaction follows the fragmentation pattern of the furazan ring with the extrusion of acetonitrile and the formation of a counterpart fragment which the nitrogen nucleophile will capture. Depending on the nature of the reagent, displacement of a fluoride anion at the C(5…
Enantioselective Synthesis of P-Chirogenic Phosphorus Compounds via the Ephedrine-Borane Complex Methodology
2008
The stereoselective synthesis of P-chirogenic organophosphorus compounds using the versatile ephedrine-methodology is reported. The principle of the method is based on the diastereoselective preparation of 1,3,2-oxazaphospholidine borane 3 from ephedrine 2 and regio- and stereoselective ring-opening of the heterocycle leading to an aminophosphine borane 4. Finally, these ring-opening products 4 are easily transformed into P-chirogenic organophosphorus compounds, by subsequent highly stereoselective reactions involving electrophilic or nucleophilic strategies.
Unravelling the mechanism of the ketene-imine Staudinger reaction. An ELF quantum topological analysis
2015
The mechanism of the ketene-imine Staudinger (KI-S) reaction between t-butyl-cyano ketene and N-phenyl phenylimine has been studied using DFT methods at the MPWB1K/6-311G(d) computational level. The reaction takes place through a two-step mechanism: (i) the first step is the nucleophilic attack of the imine nitrogen lone pair on the central carbon of the ketene yielding a zwitterionic (ZW) intermediate; (ii) the second step, which is the rate- and stereoselectivity-determining step, is a ring-closure process achieved by a nucleophilic attack of the terminal carbon atom of the ketene on the imine carbon atom. Due to the unfeasibility of a cis/trans and an E/Z stereoisomerisation at the ZW in…
Organometallic nucleophiles. Mechanism of halide displacement at saturated carbon by 2-pyridyl and 4-Pyridyl complexes [M(dmtc)(C5H4N-Cn)(L)] (M Pd…
1992
Abstract A mechanistic study is reported of nucleophilic halide substitution by pyridyl complexes [M(dmtc)C 5 H 4 N- C 2 )(L)] (M Pd or Pt; L PMe 3 , PEt 3 or PPh 3 ) and [Pd(dmtc)C 5 H 4 N- C 4 )(L)] (L PMe 3 or PPh 3 ) on organic halides XCH 2 R (X Cl or Br; R CHCH 2 , COMe, Ph, or CN) in various solvents, yielding the pyridylium derivatives [M(dmtc)1-CH 2 R)C 5 H 4 N- C 2 (L)] + and [Pd(dmtc)(1-CH 2 R)(C 5 H 4 N- C 4 (L)] + , respectively. The kinetics obey a second-order rate law: rate k 2 [XCH 2 R][Complex]. A similar rate law is observed for the analogous reactions involving 4-dimethyl-aminopyridine (4-dmapy) as the nucleophile. The effects of solvent and leaving group, a…
High Yield SNAr on 8-Halogenophenyl-BODIPY with Cyclic and Acyclic Polyamines
2014
Selective nucleophilic aromatic substitutions with several polyamines were performed in very good yields on halogeno-phenyl BODIPY derivatives containing an activating nitro group.
C−C Cross-Couplings from a Cyclometalated Au(III) C∧ N Complex: Mechanistic Insights and Synthetic Developments
2021
Abstract In recent years, the reactivity of gold complexes was shown to extend well beyond π‐activation and to hold promises to achieve selective cross‐couplings in several C−C and C−E (E=heteroatom) bond forming reactions. Here, with the aim of exploiting new organometallic species for cross‐coupling reactions, we report on the Au(III)‐mediated C(sp2)−C(sp) occurring upon reaction of the cyclometalated complex [Au(CCH2N)Cl2] (1, CCH2N=2‐benzylpyridine) with AgPhCC. The reaction progress has been monitored by NMR spectroscopy, demonstrating the involvement of a number of key intermediates, whose structures have been unambiguously ascertained through 1D and 2D NMR analyses (1H, 13C, 1H‐1H CO…